/in/foo.c: In function 'main':
/in/foo.c:9:9: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
   int m=sqrt(xx);
         ^~~~
/in/foo.c:9:9: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:9:9: note: include '<math.h>' or provide a declaration of 'sqrt'
/in/foo.c:13:6: error: 'i' undeclared (first use in this function)
   if(i!=m+1)
      ^
/in/foo.c:13:6: note: each undeclared identifier is reported only once for each function it appears in